Jim uses three logs to mark the perimeter of his triangular flower bed. One side of the flower bed is 6 feet long and another side is 9 feet long. Which could be the length in feet of the other side?

A. 2

B. 3

C. 13

D. 15

Imagine you lay the 9 and 6 logs side by side. The 6 is 3 feet short of the 9.

This rules out two as it is 1 foot short.

3 is also ruled out as there would be no dimension to the flower bed - it would be impossible to make a triangle.

Now do the reverse - use on of the remaining logs to test if they would work.

Try 15; 9 + 6 = 15 but we're looking to make a larger number

9 + 6 = 15 > 13 feet

The only log it can be is C 13 feet.